The long term goal of this proposal is to understand how antibody classes are regulated in the context of parasite immunity . Mice infected with the metacestode, Mesocestoides corti develop a hypergammaglobulinemia that is restricted to IgM and IgG1. From previous experiments, it became clear that much of the immune response is directed against molecules released from the organism. At least two of these molecules are stress proteins. As the molecules released from the organism can be used to induce an isotype restricted response in vitro, the specific aims of the proposal are designed to define associated mechanisms. First sufficient quantities of M. corti stress proteins/released molecules will be isolated using biochemical techniques and generating expression libraries. Using purified proteins, the IgG1 inducing factor will be identified. Preliminary results indicate an active release of M. corti stress proteins. Because of the known importance of stress proteins in immunity to pathogens and the potential impact of secreted molecules, the mechanism of release will be analyzed using a number of drug inhibitors. Another aim will take advantage of the large number of B cells that are activated to produce IgG1. These cells will be analyzed simultaneously for cell size and morphology , cell surface activation markers, and expression of gamma 1 germline transcripts. In this way differentiation stage(s) of B cells committed to IgGl will be defined. In addition, T cells stimulated by the organism, particularly those stimulated by the extracellular proteins, will be further analyzed for phenotype and function. Finally, the potential role of stress proteins in regulating isotype responses physiologically will be explored. These studies will provide important new insights into the regulation of antibody class expression and the effects of the stress response in infection and immunity.